The Flak 30 (Flugabwehrkanone 30) and improved Flak 38 were 20 mm anti-aircraft guns used by various German forces throughout World War II. It was not only the primary German light anti-aircraft gun, but by far the most numerously produced German artillery piece throughout the war.[1] It was produced in a variety of models, notably the Flakvierling 38 which combined four Flak 38 autocannons onto a single carriage.

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The Germans fielded the unrelated early 2 cm Flak 28 just after World War I, but the Treaty of Versailles outlawed these weapons and they were sold to Switzerland.

The original Flak 30 design was developed from the Solothurn ST-5 as a project for the Kriegsmarine, which produced the 20 mm C/30. The gun fired the "Long Solothurn", a 20 × 138 mm belted cartridge that had been developed for the ST-5 and was one of the most powerful 20 mm rounds in existence.[2]

The C/30, featuring a barrel length of 65 calibers, had a rate of about 120 rounds per minute. Disappointingly, it proved to have feeding problems and would often jam, which was offset to some degree by its undersized magazine, holding only 20 rounds, which tended to make reloading a frequent necessity anyway. Nevertheless the C/30 became the primary shipborne light AA weapon, and equipped a large variety of German ships. The C/30 was also used experimentally as an aircraft weapon, notably on the Heinkel He 112, where its high power allowed it to penetrate armored cars and the light tanks of the era during the Spanish Civil War.[citation needed]

Rheinmetall then started an adaptation of the C/30 for Army use, producing the 2 cm Flak 30. Generally similar to the C/30, the main areas of development were the mount, which was fairly compact. Set-up could be accomplished by dropping the gun to the ground off its two-wheeled carriage and leveling with hand cranks. The result was a triangular base that allowed fire in all directions.

The main problem with the design remained the fairly low rate of fire which, at 120 rpm was not particularly fast for a weapon of this caliber. Rheinmetall[N 1] responded with the 2 cm Flak 38, which was otherwise similar but increased the rate of fire to 220 rpm and slightly lowered overall weight to 420 kg. The Flak 38 was accepted as the standard Army gun in 1939, and by the Kriegsmarine as the C/38.

In order to provide airborne and mountain troops with AA capabilities, Mauser was contracted to produce a lighter version of the Flak 38, which they introduced as the 2 cm Gebirgsflak 38 (2 cm GebFlak 38). It featured a dramatically simplified mount using a tripod that raised the entire gun off the ground, which had the side benefit of allowing it to be set up on uneven surface. These changes reduced the overall weight of the gun to a mere 276.0 kg. Production started in 1941 and entered service in 1942.

A wide variety of 20x138B ammunition was manufactured to be used in 2 cm Flak weapons; some of the more commonly used types are listed on the following table.[3] Other kinds then in existence included numerous practice rounds (marked Übung or Üb. in German notation) and a number of different AP types. A high-velocity PzGr 40 round with a tungsten carbide core in an aluminium body existed in 20x138B caliber.

Even as the Flak 30 was entering service, the Luftwaffe and Army had doubts about its effectiveness, given the ever-increasing speeds of low-altitude fighter-bombers and attack aircraft. The Army in particular felt the proper solution was the introduction of the 37 mm caliber weapons they had been developing since the 1920s, which had a rate of fire about the same as the Flak 38, but fired a round with almost eight times the weight. This not only made the rounds deadlier on impact, but their higher energy and ballistic coefficient allowed them to travel to much longer distances, allowing the gun to engage targets at longer ranges. This meant it could keep enemy aircraft under fire over longer time spans.

The 20 mm weapons had always had weak development perspectives, improving just enough to keep them useful. It was something of a surprise when Rheinmetall was able to "pull a fast one" again, introducing the 2 cm Flakvierling 38, which improved the weapon just enough to make it competitive once again. The name vierling means literally "quadruplet" and refers to a four-barreled combination gun mounting — the same term was used for the suffix of the experimental HecklafetteHL 131V manned "quadmount" powered tail turret, meant for later versions and developments of the Heinkel He 177A, and on almost every heavy bomber design competing for the Luftwaffe's Amerika Bomber design competition.[4]

The Flakvierling weapon consisted of quad-mounted 2 cm Flak 38 AA guns with collapsing seats, folding handles, and ammunition racks. The mount had a triangular base with a jack at each leg for leveling the gun. The tracker traversed and elevated the mount manually using two handwheels. The gun was fired by a set of two pedals —each of which fired two diametrically opposite Flak 38s&mdash and could be operated either automatically or semi-automatically. When raised, the weapon measured 307 cm (10 feet 1 inch) high.

Each of the four mounted guns had a separate magazine that held only 20 rounds. This meant that a maximum combined rate of fire of 1,400 rounds per minute was reduced practically to 800 rounds per minute for combat use – which would still require that a magazine be replaced every six seconds, on each of the four guns. The guns could be fired in pairs (diagonally opposite) or simultaneously, in either semi-automatic or fully automatic mode. The effective vertical range was 2200 meters. It was also used just as effectively against ground targets as it was against low-flying aircraft.[5]

The gun was normally transported on a Sd. Ah. 52 trailer, and could be towed behind a variety of half-tracks or trucks, such as the Opel Blitz, SdKfz 251 and SdKfz 11. It was also mounted on half-tracks and tank bodies to produce mobile anti-aircraft vehicles, such as the SdKfz 7/1 (based on the SdKfz 7 half-track) and the Wirbelwind and original Möbelwagen prototype (both based on the Panzer IV tank). In Kriegsmarine use, it was fitted to U-boats and ships to provide short-range anti-aircraft defense, and was also employed in fixed installations around ports, harbors and other strategic naval targets. The Flakvierling was also a common fixture on trains, even on Hitler's own command train, where pairs of them were mounted on either end of a "camelback" flatbed car and then covered to make it look like a boxcar, sometimes with a pair of such twin-Flakvierling mount cars for defense, one near each end of Hitler's Führersonderzug train.

One similar weapon system to the Flakvierling gun system that was fielded by an Allied nation was the Browning M2HB "heavy-barrel"-based M45 Quadmount open turret unit, usually fitted as the main armament of the American M3 half track as the M16 Multiple Gun Motor Carriage. Other similar weapons were the British-designed, Canadian-made, jointly used quad 20mm Polsten gun system on a Maxson M55 motor-driven mount, which was built with leveling pads to be dismounted from a purpose-built trailer but often was just set onto a flatbed military truck; and the British-designed-and-used triple Oerlikon 20mm cannon system on another variant of a Maxson motor-drive mount, which normally was bolted directly to a flatbed military truck.

^The original source articles used to produce this single combined version state different companies for the manufacture of the various models. It suggested that Mauser produced all of the Flak 38 and later variants.

Gander, Terry and Chamberlain, Peter. Weapons of the Third Reich: An Encyclopedic Survey of All Small Arms, Artillery and Special Weapons of the German Land Forces 1939-1945. New York: Doubleday, 1979 ISBN 0-385-15090-3